1. W. D. SYLWESTROWICZ and H. A. ELKHOLY,J. Mater. Sci. 15 (1980) 42.
2. W. D. SYLWESTROWICZ, H. A. ELKHOLY and G. W. KAMMLOTT, ibid.14 (1979) 873.
3. L. PAULING, ?The Nature of the Chemical Bond? 3rd edition (Cornell University Press, Ithaca, New York, 1960) p. 514.
4. ?CRC Handbook of Chemistry and Physics? 58th edition, edited by R. C. Weast (CRC Press, Cleveland, Ohio, 1977?78) p. F-220.
5. ?CRC Handbook of Chemistry and Physics? 58th edition, edited by R. C. Weast (CRC Press, Cleveland, Ohio, 1977?78) p. D-77.